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Am J Physiol Cell Physiol (April 27, 2005). doi:10.1152/ajpcell.00542.2004
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Submitted on November 7, 2004
Accepted on April 19, 2005

Degradation of Extracellular ATP by the Retinal Pigment Epithelium

David Reigada1, Wennan Lu2, Xiulan Zhang3, Constantin Friedman2, Klara Pendrak4, Alice McGlinn2, Richard A Stone2, Alan M Laties2, and Claire H Mitchell1*

1 Physiology, University of Pennsylvania, Philadelphia, PA, USA
2 Ophthalmology, University of Pennsylvania, Philadelphia, PA, USA
3 Ophthalmology, University of Pennsylvania, Philadelphia, PA, USA; Zhongshan Ophthalmic Center, Sun Yat-Sen University, Guangzhou, China
4 Ophthalmology, University of Pennsylvania, Philadelphia, PA, USA; Physiology, University of Pennsylvania, Philadelphia, PA, USA

* To whom correspondence should be addressed. E-mail: chm{at}mail.med.upenn.edu.

Stimulation of ATP or adenosine receptors causes important physiologic changes in retinal pigment epithelial (RPE) cells that may influence their relationship to the adjacent photoreceptors. While RPE cells have been shown to release ATP, the regulation of extracellular ATP levels and the production of dephosphorylated purines is not clear. This study examined the degradation of ATP by RPE cells and the physiologic effects of the adenosine diphosphate (ADP) that results. ATP was readily broken down by both cultured human ARPE-19 cells and the apical membrane of fresh bovine RPE cells. The compounds ARL67156 and {beta}{gamma}mATP inhibited this degradation in both cell types. RT-PCR analysis of ARPE-19 cells found mRNA message for multiple extracellular degradative enzymes; ectonucleotide pyrophosphatase/ phosphodiesterase (eNPP)1, eNPP2 and eNPP3, the ectoATPase ecto-nucleoside triphosphate diphosphohydrolase (NTPDase)2, NTPDase3, and some message for NTPDase1. Considerable levels of ADP bathed RPE cells, consistent with a role for NTPDase2. ADP and ATP increased levels of intracellular Ca2+. Both responses were inhibited by thapsigargin and P2Y1 receptor inhibitor MRS 2179. Message for both P2Y1 and P2Y12 receptors was detected in ARPE-19 cells. These results suggest that extracellular degradation of ATP in subretinal space can result in production of ADP. This ADP can stimulate P2Y receptors and augment Ca2+ signaling in the RPE.




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